Development of HPLC Optical Purity Testing Method of Denomapine and Application to Its Photostability

Abstract

Direct enantiomer separation of denopamine (DP, active form: R (-)-form), which is an optically active and an orally administrable cardiotonic agent, was investigated by HPLC with β-cyclodextrin (β-CD) immobilized chiral stationary phases (CSPs). Successful enantiomer separation under the reversed-phase mode was achieved by a β-CD having a phenyl moiety immobilized CSP with large resolution within 10 min. Optical purity testing and assay of tablets by the HPLC method developed were validated for specificity, linearity, and recovery. Validation results indicate the method is accurate and has a good linearity and sensitivity. Limit of detection and limit of quantitation of the minor enantiomer were 0.01% and 0.03%, respectively. Assay of DP tablets 5 mg by the internal standard method was also successfully achieved within 10 min. Further, photostability of DP was evaluated by this chiral HPLC method and the reversed-phase HPLC with an ODS column. Chemical structures of two photoproducts generated in an aqueous media were determined by LC-MS/MS, showing these were p-hydroxybenzaldehyde and 3,4-dimethoxyphenethylamine. Other than these two main photoproducts, low level (0.17%) of the minor enantiomer was detected.